The Project, Mercuro-Coli

Introduction

With industrial growth, wastes are accumulating and the presence of pollutant and toxic compounds is becoming an international concern.

In this context, we present Mercuro-Coli, an easy-to-use biosensor for the in situ detection and quantification of mercury into polluted water. Intended to fieldwork applications, the device should be very easy to handle:

• Unpack the plate.
• Deposit the polluted water sample.
• If mercury is present, a red stripe appear, its position indicates the amount of pollutant.

Specifications

At the beginning of the project, we defined a certain number of specifications for the device:

• Use a single bacterial strain: Escherichia coli BW 25 113, containing the whole genetic network
• Form a biofilm on the plate with E. coli bacteria containing the designed genetic circuit.
  This point was revised according to modeling results. A device with channels containing bacteria instead of a biofilm has been chosen.

• Build a comparative measurement system:

The principle of the measurement is based on the comparison between an unknown mercury concentration and a known IPTG concentration. In practice, the quantification scale is made by the prior application of a concentration gradient of IPTG on the plate.

Two different bacterial behaviors arise from the uniform addition of polluted sample on the plate. They depend on the predominant concentration:

On the left side, where the mercury concentration is prevailing, bacteria will behave as senders. They have the ability to release quorum sensing molecules (AHL) in the external medium, thanks to the expression of the CinI protein. On the right, where the IPTG concentration is dominant, bacteria will behave as receivers. They express CinR protein, a cytoplasmic receptor for quorum sensing.
In summary, two areas with distinctive bacterial behavior appear on the plate. They are separated by one boundary that approaches one side of the plate or the other, depending on the mercury level. For example, in the case of a sample with a low mercury concentration, the boundary will appear closer to the left side.

The key point is therefore the localization of the boundary, which we need to visualize

• A visual result:

At the boundary,Quorum Sensing molecule, AHL, released by sending bacteria will be uptaken by the front of receiving bacteria. The complex formed by AHL molecules and CinR proteins will then induce the coloration of the front receiving bacteria.

Let's go further to understand how such evolution of this system is possible with only one strain ?